The present invention relates to a clarifying filter centrifuge of the type including an enclosed drum driven by a driving shaft, and a filter means positioned in a cover of the centrifuge and extending perpendicular to the axis of the driving shaft, and to a method of separating or filtering suspensions by means of said centrifuge.
There are two types of conventional centrifuges for filtering suspensions, namely solid jacket centrifuges and filter centrifuges.
Solid jacket centrifuges are utilized preferably for clarifying liquids. The heavy phase is deposited and collected on the wall of the drum while the light phase of the liquid, which is also a liquid, flows through an overflow weir.
In the filter centrifuges, the liquid flows through filter cakes and filter means. This type of centrifuge is normally applied for dehumidizing well-filtered pumps.
The specific characteristic of the clarifying filter-centrifuge resides in that the suspension is not only silted there but is also filtered. If it is desired to treat a solid-free material, for example in case of solvent agent recovery and if the suspensions are not well filtered, the application of the clarifying filter centrifuge is preferable, specifically when flocculation means are undesired due to their costs or when these means affect the following chemical process.
German Offenlegungsschrift DE-OS No. 32 38 728 discloses a centrifuge for difficultly filterable suspensions. The filtering process is carried out under superimposing of the other separation methods. The separation of the liquid from the solids is performed by the sedimentation and filtration. The centrifuge is comprised substantially of two preferably parallel plate-shaped members rigidly connected to each other and extending normal to the axis of rotation. The peripheries of these members are closed with a tubular body so that a hollow chamber for receiving a suspension to be processed is formed.
For the removal of the solids the hollow chamber is opened by the displacement of the tubular body. The separating insert which is comprised of a diaphragm, which is connected to a supporting element by a conical ring is perpendicular to the rotation axis and is secured to a ring-shaped front wall of the centrifuge chamber. The ring-shaped front wall is connected to the back wall of the chamber by three bolts inserted in protective sleeves. The suspension flows via an inlet tube to a distributor cone which accelerates suspension and leads the same to the back wall. The suspension is fed into the centrifuge until the liquid level has reached the bolts. The displacement of the solid jacket or the sleeve for the unloading of solids from the centrifuge is carried out by a pneumatic cylinder which transmits a displacement force of a system operated outside to a rotating system via ball bearings. Also a centrifugal force which is required to lock up the centrifuge while operating is applied by that cylinder. Another version utilizes vacuum and pressure air which are supplied via the centrifuge shaft between the back wall of the chamber and drum body for the closing or opening of the centrifuge.
The disadvantages of this conventional centrifuge are as follows:
The centrifuge chamber, at the seal place between the drum and the cover, is subjected to the action of a small force to lock up the centrifuge of the pneumatic device or vacuum, and if the sealing of the centrifuge is not tight enough the suspension liquid flows into the solid material and the separated material becomes moist.
Further, during the high-speed centrifugal process the relatively high force for locking applied via the ball bearings leads to failure of the ball bearings.
The conical shape of the clamping ring of the filter means leads to folding of the filter means whereby the filter means can no longer be reliably stretched.
The clmaping of the filter means is not suitable to various thicknesses of the filter means because the clamping and the diaphragm rings must be precisely adjusted.
If, due to manufacture tolerances of the clamping ring and diaphragm ring and manufacture tolerances of the thickness of the filter means, the diaphragm ring is not precisely positioned on the membrane this would cause leakage at the worn-off places between the drum and the cover of the centrifuge.
Due to wear it has been required that sealings between the wall of the chamber of the centrifuge and drum sleeve be non-tight so that suspension would penetrate the chamber between the back wall of the centrifuge and the bottom wall of the drum which, on the one hand, was prevented by leakage of vacuum pressure for the centrifugal process and, on the other hand, caused the formation of radiation nests during the filtering of radio-active suspensions. Furthermore, this undesired breakoff during filtering of suspensions which contain ferments or the like materials causes non-desired residues to be deposited in the centrifuge chamber which would require dismantling and cleaning of the centrifuge.
Sealing materials and shapes utilized in conventional centrifuges of the type under discussion are not suitable for sealing pharmaceutical, life-supporting, radiation-active or chemically aggressive suspensions. They are also unsuitable with high pressures which occur due to liquid pressure of suspensions treated at high speeds.
Metal components utilized in such centrifuges are not sufficiently stable for filtering radioactive or chemically aggressive suspensions.
Therefore for unloading solids obtained in a centrifuging process the durm is displaced, and an enlarged projecting length of the driving shaft between the bearing and the drum bottom wall is obtained over the drum displacement path, which affects center of mass of the protruding components such as the drum chamber walls. Centrifugal materials are affected by unfavorable bearing loads or shaft loads and critical speeds so that high speeds can not be adjusted to filtering of heavier materials.
The overflow is not separated from the clarified suspension, and during the overfilling of the centrifuge it causes contamination of the filtrate.
The liquid and solid amounts in the centrifuge are visually controlled by operators, this however is non-allowable when radioactive or toxic suspensions are treated.
The housing of the centrifuge is open for feeding the suspension thereinto so that processing of the radiation-active or toxic suspensions leads to affecting the personnel and the environment.
The machine must be manually controlled during its entire operation cycle which is undesired specifically with radioactive suspensions.